Augmented drive of compressors via differential and multistage turbine

ABSTRACT

A method of distributing power within a gas turbine engine is disclosed. In various embodiments, the method includes driving a high pressure turbine having a first stage and a second stage with an exhaust stream from a combustor, the first stage connected to a high pressure turbine first stage spool and the second stage connected to a high pressure turbine second stage spool; driving a high pressure compressor connected to a high pressure compressor spool via a differential system, the differential system having a first stage input gear connected to the high pressure turbine first stage spool, a second stage input gear connected to the high pressure turbine second stage spool and an output gear assembly connected to the high pressure compressor spool; and selectively applying an auxiliary input power into at least one of the high pressure compressor spool and the high pressure turbine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority toU.S. Prov. Appl. 62/890,825, entitled “AUGMENTED DRIVE OF COMPRESSORSVIA DIFFERENTIAL AND MULTISTAGE TURBINE,” filed Aug. 23, 2019, U.S.Prov. Appl. 62/890,836, entitled “MULTISTAGE GAS TURBINE ENGINE WITHTORQUE CONVERTER DRIVE OF COMPRESSOR,” filed Aug. 23, 2019, and U.S.Prov. Appl. 62/890,848, entitled “MULTISTAGE GAS TURBINE ENGINE WITHDIFFERENTIAL DRIVE OF COMPRESSOR,” filed Aug. 23, 2019, the entirety ofeach of which is hereby incorporated by reference herein for allpurposes.

FIELD

The present disclosure relates generally to gas turbine engines and,more particularly, to gas turbine engines having a multistage turbinesection configured to drive a compressor section.

BACKGROUND

Gas turbine engines typically include a fan section, a compressorsection, a combustor section and a turbine section. During operation,air is pressurized in the compressor section and mixed with fuel andburned in the combustor section to generate hot combustion gases. Thehot combustion gases are then communicated through the turbine section,where energy is extracted from the hot combustion gases to power thecompressor section, the fan section or various other loads developedwithin or outside the gas turbine engine.

Spools are typically used to connect components of the turbine sectionwith components of the compressor section and the fan section. Forexample, a low speed spool generally includes an inner shaft thatinterconnects a fan, a low pressure compressor and a low pressureturbine. The inner shaft may be connected to the fan through a speedchange mechanism to drive the fan at a lower speed than that of the lowspeed spool. A high speed spool generally includes an outer shaft thatinterconnects a high pressure compressor and a high pressure turbine.The inner shaft and the outer shaft are typically concentric withrespect to one another and rotate via bearing systems about a centrallongitudinal axis, which is collinear with longitudinal axes of both thelow and high speed spools.

The high pressure turbine sections of various gas turbine engines havetwo or more stages. For example, a two-stage high pressure turbineincludes a first stage configured to receive the hot combustion gasesfrom the combustor section and a second stage configured to receive theexhaust from the first stage. In such configurations, which may rotateon the order of 20,000 rpm (≅2100 rad/sec) or greater during operation,the first stage may exhibit lower turbine efficiencies than the secondstage. Further, rotational speeds of the second stage may be limited byallowable stress limits within the blades (e.g., maximum centrifugalstress states or AN² limits). The rotational speed limits placed on thesecond stage may also impact the efficiency of the high pressurecompressor, as its design speed may be greater than the maximumrotational speed of the second stage of the high pressure turbine.Maximizing the competing efficiencies and design speeds of the highpressure compressor and the high pressure turbine, typically connectedby a common high speed spool, presents design challenges.

SUMMARY

A method of distributing power within a gas turbine engine is disclosed.In various embodiments, the method includes driving a high pressureturbine having a first stage and a second stage with an exhaust streamfrom a combustor, the first stage connected to a high pressure turbinefirst stage spool and the second stage connected to a high pressureturbine second stage spool; driving a high pressure compressor connectedto a high pressure compressor spool via a differential system, thedifferential system having a first stage input gear connected to thehigh pressure turbine first stage spool, a second stage input gearconnected to the high pressure turbine second stage spool and an outputgear assembly connected to the high pressure compressor spool; andselectively applying an auxiliary input power into at least one of thehigh pressure compressor spool and the high pressure turbine.

In various embodiments, the selectively applying the auxiliary inputpower includes applying a first input power to a first motor-generatorconnected to the high pressure compressor spool. In various embodiments,the selectively applying the auxiliary input power includes applying asecond input power to a second motor-generator connected to the highpressure turbine second stage spool. In various embodiments, theselectively applying the auxiliary input power includes applying a firstinput power to a first motor-generator connected to the high pressurecompressor spool and a second input power to a second motor-generatorconnected to the high pressure turbine second stage spool.

In various embodiments, the method includes selectively extracting anauxiliary output power from at least one of the high pressure compressorspool and the high pressure turbine. In various embodiments, theselectively extracting the auxiliary output power includes charging astorage device. In various embodiments, the selectively extracting theauxiliary output power includes extracting a first output power from afirst motor-generator connected to the high pressure compressor spool.In various embodiments, the selectively extracting the auxiliary outputpower includes extracting a second output power from a secondmotor-generator connected to the high pressure turbine second stagespool. In various embodiments, the selectively extracting the auxiliaryoutput power includes extracting a first output power from a firstmotor-generator connected to the high pressure compressor spool and asecond output power from a second motor-generator connected to the highpressure turbine second stage spool.

In various embodiments, the auxiliary input power comprises anelectrical power from a storage device. In various embodiments, theauxiliary input power enables a reduced fuel power used to drive thehigh pressure turbine.

A gas turbine engine is disclosed. In various embodiments, the gasturbine engine includes a turbine having a first stage and a secondstage, the first stage connected to a first stage spool and the secondstage connected to a second stage spool; a compressor connected to acompressor spool; a differential system having a first stage input gearconnected to the first stage spool, a second stage input gear connectedto the second stage spool and an output gear assembly connected to thecompressor spool; and an augmentation system configured to input powerinto at least one of the high pressure compressor spool and the highpressure turbine.

In various embodiments, the differential system is configured to drivethe compressor spool in response to the first stage spool and the secondstage spool rotating at different speeds with respect to a centrallongitudinal axis. In various embodiments, the differential system isconfigured to input a first stage spool rotational speed and a secondstage spool rotational speed and output a compressor spool rotationalspeed having a value in between the first stage spool rotational speedand the second stage spool rotational speed. In various embodiments, thedifferential system is configured to input a first stage spoolrotational speed greater than a second stage spool rotational speed andoutput a compressor spool rotational speed having a value in between thefirst stage spool rotational speed and the second stage spool rotationalspeed.

In various embodiments, the augmentation system includes a firstmotor-generator connected to the compressor spool and a secondmotor-generator connected to the second stage spool. In variousembodiments, the first motor-generator and the second motor-generatoreach include a stator connected to an engine static structure.

A method for distributing power from a turbine section of a gas turbineengine is disclosed. In various embodiments, the method includesgenerating a first stage rotational power from a first stage of theturbine section; generating a second stage rotational power from asecond stage of the turbine section; inputting into a differentialsystem the first stage rotational power via a first stage spool and thesecond stage rotational power via a second stage spool; outputting fromthe differential system a compressor stage rotational power configuredto drive a compressor spool of the gas turbine engine; and selectivelyapplying an auxiliary input power into at least one of the compressorspool, the first stage spool and the second stage spool. In variousembodiments, the method includes selectively extracting an auxiliaryoutput power from at least one of the compressor spool, the first stagespool and the second stage spool. In various embodiments, the methodincludes driving a fan via a low pressure turbine of the turbinesection.

The forgoing features and elements may be combined in any combination,without exclusivity, unless expressly indicated herein otherwise. Thesefeatures and elements as well as the operation of the disclosedembodiments will become more apparent in light of the followingdescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the following detailed description andclaims in connection with the following drawings. While the drawingsillustrate various embodiments employing the principles describedherein, the drawings do not limit the scope of the claims.

FIG. 1A is a schematic view of a gas turbine engine, in accordance withvarious embodiments;

FIG. 1B is a schematic view of a differential system for a gas turbineengine, in accordance with various embodiment;

FIG. 2A is a schematic view of a gas turbine engine, in accordance withvarious embodiments;

FIG. 2B is a schematic view of a differential system for a gas turbineengine, in accordance with various embodiment;

FIG. 3A is a schematic view of a gas turbine engine, in accordance withvarious embodiments;

FIG. 3B is a schematic view of a differential system for a gas turbineengine, in accordance with various embodiment;

FIG. 4A is a schematic view of a gas turbine engine, in accordance withvarious embodiments;

FIG. 4B is a schematic view of a differential system for a gas turbineengine, in accordance with various embodiment;

FIG. 5 describes various method steps for powering a high pressurecompressor of a gas turbine engine, in accordance with variousembodiments;

FIGS. 6A and 6B graphically illustrate a high pressure compressor powerversus a high pressure turbine power, in accordance with variousembodiments; and

FIGS. 7A and 7B graphically illustrate a high pressure compressor powerversus a high pressure turbine power, in accordance with variousembodiments.

DETAILED DESCRIPTION

The following detailed description of various embodiments herein makesreference to the accompanying drawings, which show various embodimentsby way of illustration. While these various embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that changes may be made without departing from the scopeof the disclosure. Thus, the detailed description herein is presentedfor purposes of illustration only and not of limitation. Furthermore,any reference to singular includes plural embodiments, and any referenceto more than one component or step may include a singular embodiment orstep. Also, any reference to attached, fixed, connected, or the like mayinclude permanent, removable, temporary, partial, full or any otherpossible attachment option. Additionally, any reference to withoutcontact (or similar phrases) may also include reduced contact or minimalcontact. It should also be understood that unless specifically statedotherwise, references to “a,” “an” or “the” may include one or more thanone and that reference to an item in the singular may also include theitem in the plural. Further, all ranges may include upper and lowervalues and all ranges and ratio limits disclosed herein may be combined.

Referring now to the drawings, FIGS. 1A and 1B schematically illustratesa gas turbine engine 100, in accordance with various embodiments. Thegas turbine engine 100 is disclosed herein as a four-spool turbofanengine that generally incorporates a fan section 102, a compressorsection 104, a combustor section 106 and a turbine section 108. The fansection 102 drives air along a bypass flow path B in a bypass ductdefined by a radially inner surface of a nacelle 110 and a radiallyouter surface of a core engine case 112, while the compressor section104 drives air along a core flow path C for compression andcommunication into the combustor section 106 and then expansion throughthe turbine section 108. The core flow path C is generally ductedthrough a core duct, which may be defined by the compressor, combustorand turbine sections, radially inward of the core engine case 112. Thecore duct may also be defined, in part, by a forward strut 111, anintermediate strut 113 and an exit strut 117, each of which may alsofunction as a vane or duct and be formed as part of or connected to afixed structure for various of the rotating components of the gasturbine engine 100.

More specifically, the fan section 102 includes a fan 114, thecompressor section 104 includes a high pressure compressor 116, thecombustor section 106 includes a combustor 118 and the turbine section108 includes a high pressure turbine 120 and a low pressure turbine 122.Further, the high pressure turbine 120 includes a first stage 124 and asecond stage 126 disposed downstream of the first stage 124. In general,air in the core flow path C is compressed by the high pressurecompressor 116, mixed and burned with fuel in the combustor 118, andthen expanded over the high pressure turbine 120 and the low pressureturbine 122, with the high pressure turbine 120 and the low pressureturbine 122 being configured, as described below, to drive the highpressure compressor 116 and the fan 114.

Still referring to FIGS. 1A and 1B, in various embodiments, the gasturbine engine 100 includes a low speed spool 128, a high pressureturbine first stage spool 130 (or a first stage spool), a high pressureturbine second stage spool 132 (or a second stage spool) and a highpressure compressor spool 134 (or a compressor spool). Each of thespools is generally situated within a bearing assembly 136, componentsof which are housed within or connected to an engine static structure138, and configured to rotate coaxially with respect to a centrallongitudinal axis A. The low speed spool 128 is configured to connectthe fan 114 to the low pressure turbine 122. While the low speed spool128 is illustrated as directly connecting the fan 114 and the lowpressure turbine 122, it will be appreciated that various interveningdrive systems, such as, for example, a fan drive gear system may beincorporated into the gas turbine engine 100 such that the fan 114rotates at a lower speed than does the low speed spool 128. The highpressure turbine first stage spool 130 and the high pressure turbinesecond stage spool 132 are configured to drive the high pressurecompressor 116, which is mounted on the high pressure compressor spool134, via a differential system 140.

In addition, the gas turbine engine 100 includes an augmentation systemwhich, in various embodiments, may include one or more motor-generatorsconfigured to input power to or extract power from various of the spoolswithin the gas turbine engine 100. For example, in various embodiments,a first motor-generator 160 is connected to the high pressure compressorspool 134 and a second motor-generator 162 is connected to the highpressure turbine second stage spool 132. In various embodiments, thefirst motor-generator 160 may comprise an armature 180 that is connectedto the high pressure compressor spool 134 and a stator 181 that isconnected to the engine static structure 138. Similarly, in variousembodiments, the second motor-generator 162 may comprise an armature 182that is connected to the high pressure turbine second stage spool 132and a stator 183 that is connected to the engine static structure 138.The first motor-generator 160 is connected to and controlled by a firstcontroller 164 and the second motor-generator 162 is connected to andcontrolled by a second controller 166. In various embodiments, the firstcontroller 164 and the second controller 166 are further controlled by afull authority digital electric controller or FADEC 168. While the firstcontroller 164, the second controller 166 and the FADEC 168 areillustrated as individual components, the disclosure contemplatescontrol of the first motor-generator 160 and the second motor-generator162 being accomplished by a controller 170, which may be considered toinclude combined functionalities of one or more of the first controller164, the second controller 166 and the FADEC 168. In variousembodiments, an energy storage device 172 is also included within thegas turbine engine 100. The energy storage device 172 may comprise, forexample, a battery, a capacitor or any similar rechargeable energystorage component. In various embodiments, the energy storage device 172may also comprise or be connected to an auxiliary source of power, suchas, for example, an auxiliary power unit or APU 174.

In various embodiments, the controller 170 is configured to monitor andcontrol operation of the first motor-generator 160 and the secondmotor-generator 162, based on whether one or both of themotor-generators are required to drive the spool to which it isattached, to generate power for storage in the energy storage device 172or to carry out load-sharing between the various spools and thecomponents attached thereto. For example, in various embodiments, thefirst motor-generator 160 may be employed to increase (or maintain) therotational speed of the high pressure compressor spool 134 by providingpower to the first motor-generator 160 (i.e., the motor-generator isbeing used as a motor). In various embodiments, the firstmotor-generator 160 may also be employed to decrease (or maintain) therotational speed of the high pressure compressor spool 134 by extractingpower from the first motor-generator 160 (i.e., the motor-generator isbeing used as a generator). Similarly, in various embodiments, thesecond motor-generator 162 may be employed to increase (or maintain) therotational speed of the high pressure turbine second stage spool 132 byproviding power to the second motor-generator 162 (i.e., themotor-generator is being used as a motor). In various embodiments, thesecond motor-generator 162 may also be employed to decrease (ormaintain) the rotational speed of the high pressure turbine second stagespool 132 by extracting power from the second motor-generator 162 (i.e.,the motor-generator is being used as a generator).

Referring more specifically, to FIG. 1B, the differential system 140includes a first stage input gear 142, a second stage input gear 144 andan output gear 146, where the first stage input gear 142 and the secondstage input gear 144 are sized the same (e.g., the gears share the samenumber of teeth and the same radius). As illustrated, the first stageinput gear 142 is connected to and rotates with the high pressureturbine first stage spool 130. Similarly, the second stage input gear144 is connected to and rotates with the high pressure turbine secondstage spool 132. The output gear 146 is connected to the high pressurecompressor spool 134 via a shaft 148 or similar mechanism and is drivenby the first stage input gear 142 via a first bevel gear connection 150and the second stage input gear 144 via a second bevel gear connection152. Unlike the first stage input gear 142 and the second stage inputgear 144, both of which are configured to rotate about the centrallongitudinal axis A, the output gear 146, together with the shaft 148(the combination of which, in various embodiments, is referred to as anoutput gear assembly), is configured to revolve about the centrallongitudinal axis A in response to being driven by the first stage inputgear 142 and the second stage input gear 144. Further, because theoutput gear 146 is coupled to the high pressure compressor spool 134 viathe shaft 148, the rotational speed of the high pressure compressorspool 134 about the central longitudinal axis A will be the same as thespeed at which the output gear 146 revolves about the centrallongitudinal axis A. In addition, as illustrated, the differentialsystem 140 includes a first differential subassembly 141 ₁ thatcomprises the various gears just described. In various embodiments,however, the differential system 140 may comprise any number ofdifferential subassemblies, including, for example, a seconddifferential subassembly 141 ₂, with each of the various differentialsubassemblies being generally spaced about the central longitudinal axisA.

Still referring to FIGS. 1A and 1B, various operational aspects aredescribed. Assume, for example, the high pressure turbine first stagespool 130, together with the first stage input gear 142, rotate at afirst stage spool rotational speed of N_(HPT1), and the high pressureturbine second stage spool 132, together with the second stage inputgear 144, rotate at a second stage spool rotational speed of N_(HPT2).With such assumptions, the high pressure compressor spool 134 willrotate at a high pressure compressor spool rotational speed of N_(HPC)(or a compressor spool rotational speed), which may be expressed by therelation N_(HPC)=(N_(HPT1)+N_(HPT2))/2. Thus, where the high pressureturbine first stage spool 130 and the high pressure turbine second stagespool 132 are configured to corotate (i.e., rotate in the same directionabout the central longitudinal axis A), the high pressure compressorspool rotational speed, N_(HPC), is simply the arithmetic mean of thetwo input rotational speeds. Or, in other words, the differential system140, as described above, operates as a summer device that is configuredto split the input rotational speeds of the high pressure turbine firststage spool 130 and the high pressure turbine second stage spool 132.Such configuration enables the first stage 124 of the high pressureturbine 120, the second stage 126 of the high pressure turbine 120 andthe high pressure compressor 116 to rotate at different speeds, suchthat, for example, N_(HPT1)>N_(HPC)>N_(HPT2). Advantageously, theconfiguration enables the high pressure compressor 116 to rotate at aspeed having a value greater than that which might otherwise be limitedby maximum allowable stress limits within the blades of the second stage126 of the high pressure turbine 120 (e.g., maximum centrifugal stressstates or AN² limits). Further, the configuration enables the firststage 124 of the high pressure turbine 120 to rotate at a speed having avalue greater than both those of the high pressure compressor 116 andthe second stage 126 of the high pressure turbine 120, enabling thefirst stage 124 to operate at a higher efficiency than that which mightotherwise be limited by efficiency or stress considerations of theaforementioned rotating components. Also, in various embodiments, thefan 114 will rotate at a speed equal to that of the low pressure turbine122 via the low speed spool 128.

Consistent with the foregoing description, in various embodiments, thefirst motor-generator 160 and the second motor-generator 162 may beemployed to adjust—e.g., to increase or decrease—one or both of N_(HPC)and N_(HPT2), respectively, by operating one or both of the respectivemotor-generators in either a motor-mode or a generator-mode. Forexample, during transient operation of the gas turbine engine 100—e.g.,during a takeoff or an acceleration in flight—increasing the speed ofone or both of N_(HPC) and N_(HPT2) may result in increased power orefficiency of the engine without approaching or reaching the applicablemaximum centrifugal stress states or AN² limits of the turbine blades,for example, in the second stage 126 of the high pressure turbine 120.On the other hand, during steady state operation—e.g., during cruise ataltitude—adjusting the speed of one or both of N_(HPC) and N_(HPT2) mayresult in increased efficiency of the engine and the ability to generatepower for storage in the storage device.

Referring now to FIGS. 2A and 2B, a gas turbine engine 200 isillustrated, in accordance with various embodiments. As illustrated, thegas turbine engine 200 shares certain of the structural characteristicsof the gas turbine engine 100 described above with reference to FIGS. 1Aand 1B, a principal exception being the addition of a low pressurecompressor 215 to the gas turbine engine 200. Similar to the descriptionabove, the gas turbine engine 200 is a four-spool turbofan engine thatgenerally incorporates a fan section 202, a compressor section 204, acombustor section 206 and a turbine section 208. The fan section 202drives air along a bypass flow path B in a bypass duct defined by aradially inner surface of a nacelle 210 and a radially outer surface ofa core engine case 212, while the compressor section 204 drives airalong a core flow path C for compression and communication into thecombustor section 206 and then expansion through the turbine section208. The core flow path C is generally ducted through a core duct, whichmay be defined by the compressor, combustor and turbine sections,radially inward of the core engine case 212. The core duct may also bedefined, in part, by a forward strut 211, an intermediate strut 213 andan exit strut 217, each of which may also function as a vane or duct andbe formed as part of or connected to a fixed structure for various ofthe rotating components of the gas turbine engine 200.

More specifically, the fan section 202 includes a fan 214, thecompressor section 204 includes the low pressure compressor 215, a highpressure compressor 216, the combustor section 206 includes a combustor218 and the turbine section 208 includes a high pressure turbine 220 anda low pressure turbine 222. Further, the high pressure turbine 220includes a first stage 224 and a second stage 226 disposed downstream ofthe first stage 224. In general, air in the core flow path C iscompressed, first by the low pressure compressor 215 and then by thehigh pressure compressor 216, mixed and burned with fuel in thecombustor 218, and then expanded over the high pressure turbine 220 andthen the low pressure turbine 222, with the high pressure turbine 220and the low pressure turbine 222 being configured, as described below,to drive the low pressure compressor 215, the high pressure compressor216 and the fan 214.

Still referring to FIGS. 2A and 2B, in various embodiments, the gasturbine engine 200 includes a low speed spool 228, a high pressureturbine first stage spool 230, a high pressure turbine second stagespool 232 and a high pressure compressor spool 234. Each of the spoolsis generally situated within a bearing assembly 236, components of whichare housed within or connected to an engine static structure 238, andconfigured to rotate coaxially with respect to a central longitudinalaxis A. The low speed spool 228 is configured to connect the fan 214 tothe low pressure turbine 222. While the low speed spool 228 isillustrated as directly connecting the fan 214 and the low pressureturbine 222, it will be appreciated that various intervening drivesystems, such as, for example, a fan drive gear system may beincorporated into the gas turbine engine 200 such that the fan 214rotates at a lower speed than does the low speed spool 228. The highpressure turbine first stage spool 230 and the high pressure turbinesecond stage spool 232 are configured to drive the high pressurecompressor 216, which is mounted on the high pressure compressor spool234, via a differential system 240. The high pressure turbine secondstage spool 232 is also configured to rotate the low pressure compressor215.

In addition, the gas turbine engine 200 includes an augmentation systemwhich, in various embodiments, may include one or more motor-generatorsconfigured to input power to or extract power from various of the spoolswithin the gas turbine engine 200. For example, in various embodiments,a first motor-generator 260 is connected to the high pressure compressorspool 234, a second motor-generator 262 is connected to the highpressure turbine second stage spool 232 and a third motor-generator 261is connected to the low speed spool 228 and to the high pressure turbinesecond stage spool 232. In various embodiments, the firstmotor-generator 260 may comprise an armature 280 that is connected tothe high pressure compressor spool 234 and a stator 281 that isconnected to the engine static structure 238. Similarly, in variousembodiments, the second motor-generator 262 may comprise an armature 282that is connected to the high pressure turbine second stage spool 232and a stator 283 that is connected to the engine static structure 238.Also, in various embodiments, the third motor-generator 261 may comprisean armature 284 that is connected to the high pressure turbine secondstage spool 232 and a stator 285 that is connected to the low speedspool 228, enabling both the armature 284 and the stator 285 to rotate,but at different speeds such that a motor-like or generator-likeoperation may be affected between the high pressure turbine second stagespool 232 and the low speed spool 228. The first motor-generator 260 isconnected to and controlled by a first controller 264, the secondmotor-generator 262 is connected to and controlled by a secondcontroller 266 and the third motor-generator 261 is connected to andcontrolled by a third controller 265. In various embodiments, the firstcontroller 264, the second controller 266 and the third controller 265are further controlled by a full authority digital electric controlleror FADEC 268. While the first controller 264, the second controller 266,the third controller 265 and the FADEC 268 are illustrated as individualcomponents, the disclosure contemplates control of the firstmotor-generator 260, the second motor-generator 262 and the thirdmotor-generator 261 being accomplished by a controller 270, which may beconsidered to include combined functionalities of one or more of thefirst controller 264, the second controller 266, the third controller265 and the FADEC 268. In various embodiments, an energy storage device272 is also included within the gas turbine engine 200. The energystorage device 272 may comprise, for example, a battery, a capacitor orany similar rechargeable energy storage component. In variousembodiments, the energy storage device 272 may also comprise or beconnected to an auxiliary source of power, such as, for example, anauxiliary power unit or APU 274.

In various embodiments, the controller 270 is configured to monitor andcontrol operation of the first motor-generator 260, the secondmotor-generator 262 and the third motor-generator 261, based on whetherone or more of the motor-generators are required to drive the spool towhich it is attached, to generate power for storage in the energystorage device 272 or to carry out load-sharing between the variousspools and the components attached thereto. For example, in variousembodiments, the first motor-generator 260 may be employed to increase(or maintain) the rotational speed of the high pressure compressor spool234 by providing power to the first motor-generator 260 (i.e., themotor-generator is being used as a motor). In various embodiments, thefirst motor-generator 260 may also be employed to decrease (or maintain)the rotational speed of the high pressure compressor spool 234 byextracting power from the first motor-generator 260 (i.e., themotor-generator is being used as a generator). Similarly, in variousembodiments, the second motor-generator 262 may be employed to increase(or maintain) the rotational speed of the high pressure turbine secondstage spool 232 by providing power to the second motor-generator 262(i.e., the motor-generator is being used as a motor). In variousembodiments, the second motor-generator 262 may also be employed todecrease (or maintain) the rotational speed of the high pressure turbinesecond stage spool 232 by extracting power from the secondmotor-generator 262 (i.e., the motor-generator is being used as agenerator). In addition, in various embodiments, the thirdmotor-generator 261 may be employed to increase (or maintain) therotational speed of the high pressure turbine second stage spool 232 byproviding power to the third motor-generator 261 (i.e., themotor-generator is being used as a motor). In various embodiments, thethird motor-generator 261 may also be employed to decrease (or maintain)the rotational speed of the high pressure turbine second stage spool 232by extracting power from the third motor-generator 261 (i.e., themotor-generator is being used as a generator).

Referring more specifically, to FIG. 2B, the differential system 240includes a first stage input gear 242, a second stage input gear 244 andan output gear 246, where the first stage input gear 242 and the secondstage input gear 244 are sized the same (e.g., the gears share the samenumber of teeth and the same radius). As illustrated, the first stageinput gear 242 is connected to and rotates with the high pressureturbine first stage spool 230. Similarly, the second stage input gear244 is connected to and rotates with the high pressure turbine secondstage spool 232. The output gear 246 is connected to the high pressurecompressor spool 234 via a shaft 248 or similar mechanism and is drivenby the first stage input gear 242 via a first bevel gear connection 250and the second stage input gear 244 via a second bevel gear connection252. Unlike the first stage input gear 242 and the second stage inputgear 244, both of which are configured to rotate about the centrallongitudinal axis A, the output gear 246, together with the shaft 248(the combination of which, in various embodiments, is referred to as anoutput gear assembly), is configured to revolve about the centrallongitudinal axis A in response to being driven by the first stage inputgear 242 and the second stage input gear 244. Further, because theoutput gear 246 is coupled to the high pressure compressor spool 234 viathe shaft 248, the rotational speed of the high pressure compressorspool 234 about the central longitudinal axis A will be the same as thespeed at which the output gear 246 revolves about the centrallongitudinal axis A. In addition, as illustrated, the differentialsystem 240 includes a first differential subassembly 241 ₁ thatcomprises the various gears just described. In various embodiments,however, the differential system 240 may comprise any number ofdifferential subassemblies, such as, for example, a second differentialsubassembly 241 ₂, with each of the various differential subassembliesbeing generally spaced about the central longitudinal axis A.

Still referring to FIGS. 2A and 2B, various operational aspects aredescribed that are similar to the operational aspects described abovewith reference to FIGS. 1A and 1B. Assume, for example, the highpressure turbine first stage spool 230, together with the first stageinput gear 242, rotate at a first stage spool rotational speed ofN_(HPT1), and the high pressure turbine second stage spool 232, togetherwith the second stage input gear 244, rotate at a second stage spoolrotational speed of N_(HPT2). With such assumptions, the high pressurecompressor spool 234 will rotate at a high pressure compressor spoolrotational speed of N_(HPC), which may be expressed by the relationN_(HPC)=(N_(HPT1)+N_(HPT2))/2. Thus, where the high pressure turbinefirst stage spool 230 and the high pressure turbine second stage spool232 are configured to corotate (i.e., rotate in the same direction aboutthe central longitudinal axis A), the high pressure compressor spoolrotational speed, N_(HPC), is simply the arithmetic mean of the twoinput rotational speeds. Or, in other words, the differential system240, as described above, operates as a summer device that is configuredto split the input rotational speeds of the high pressure turbine firststage spool 230 and the high pressure turbine second stage spool 232.Such configuration enables the first stage 224 of the high pressureturbine 220, the second stage 226 of the high pressure turbine 220, thelow pressure compressor 215 and the high pressure compressor 216 torotate at different speeds, such that, for example,N_(HPT1)>N_(HPC)>N_(HPT2). Similar to the discussion above, theconfiguration enables the high pressure compressor 216 to rotate at aspeed greater than that which might otherwise be limited by maximumallowable stress limits within the blades of the second stage 226 of thehigh pressure turbine 220 (e.g., maximum centrifugal stress states orAN² limits). Further, the configuration enables the first stage 224 ofthe high pressure turbine 220 to rotate at a speed greater than boththose of the high pressure compressor 216 and the second stage 226 ofthe high pressure turbine 220, enabling the first stage 224 to operateat a higher efficiency than that which might otherwise be limited byefficiency or stress considerations of the aforementioned rotatingcomponents. Also, in various embodiments, the fan 214 will rotate at aspeed equal to that of the low pressure turbine 222 via the low speedspool 228, while the low pressure compressor 215 will rotate at a speedequal to N_(HPT2) via the high pressure turbine second stage spool 232.

Consistent with the foregoing description, in various embodiments, thefirst motor-generator 260, the second motor-generator 262 and the thirdmotor-generator 261 may be employed to adjust—e.g., to increase ordecrease—one or both of N_(HPC) and N_(HPT2), respectively, by operatingone or more of the respective motor-generators in either a motor-mode ora generator-mode. For example, during transient operation of the gasturbine engine 200—e.g., during a takeoff or an acceleration inflight—increasing the speed of one or both of N_(HPC) and N_(HPT2) mayresult in increased power or efficiency of the engine withoutapproaching or reaching the applicable maximum centrifugal stress statesor AN² limits of the turbine blades, for example, in the second stage226 of the high pressure turbine 220. On the other hand, during steadystate operation—e.g., during cruise at altitude—adjusting the speed ofone or both of N_(HPC) and N_(HPT2) may result in increased efficiencyof the engine and the ability to generate power for storage in thestorage device. Further, in various embodiments and as illustrated anddescribed herein, where the rotational speed of the low pressurecompressor 215, N_(LPC), is less than N_(HPC), and the low pressurecompressor 215 is not coupled to the fan 214 (e.g., through a shaft orfan drive gear system connected to the low pressure compressor 215),N_(LPC) becomes independent of the rotational speed of the fan 214,N_(FAN). This facilitates an increase in the pressure ratio across thelow pressure compressor 215, leading to an increase in the overallpressure ratio across the compressor section 204, including both the lowpressure compressor 215 and the high pressure compressor 216.

Referring now to FIGS. 3A and 3B a gas turbine engine 300 isillustrated, in accordance with various embodiments. The gas turbineengine 300 is disclosed herein as a four-spool turbofan engine thatgenerally incorporates a fan section 302, a compressor section 304, acombustor section 306 and a turbine section 308. The fan section 302drives air along a bypass flow path B in a bypass duct defined by aradially inner surface of a nacelle 310 and a radially outer surface ofa core engine case 312, while the compressor section 304 drives airalong a core flow path C for compression and communication into thecombustor section 306 and then expansion through the turbine section308. The core flow path C is generally ducted through a core duct, whichmay be defined by the compressor, combustor and turbine sections,radially inward of the core engine case 312. The core duct may also bedefined, in part, by a forward strut 311, an intermediate strut 313 andan exit strut 317, each of which may also function as a vane or duct andbe formed as part of or connected to a fixed structure for various ofthe rotating components of the gas turbine engine 300.

More specifically, the fan section 302 includes a fan 314, thecompressor section 304 includes a high pressure compressor 316, thecombustor section 306 includes a combustor 318 and the turbine section308 includes a high pressure turbine 320 and a low pressure turbine 322.Further, the high pressure turbine 320 includes a first stage 324 and asecond stage 326 disposed downstream of the first stage 324. In general,air in the core flow path C is compressed by the high pressurecompressor 316, mixed and burned with fuel in the combustor 318, andthen expanded over the high pressure turbine 320 and the low pressureturbine 322, with the high pressure turbine 320 and the low pressureturbine 322 being configured, as described below, to drive the highpressure compressor 316 and the fan 314.

Still referring to FIGS. 3A and 3B, in various embodiments, the gasturbine engine 300 includes a low speed spool 328, a high pressureturbine first stage spool 330 (or a first stage spool), a high pressureturbine second stage spool 332 (or a second stage spool) and a highpressure compressor spool 334 (or a compressor spool). Each of thespools is generally situated within a bearing assembly 336, componentsof which are housed within or connected to an engine static structure338, and configured to rotate coaxially with respect to a centrallongitudinal axis A. The low speed spool 328 is configured to connectthe fan 314 to the low pressure turbine 322. While the low speed spool328 is illustrated as directly connecting the fan 314 and the lowpressure turbine 322, it will be appreciated that various interveningdrive systems, such as, for example, a fan drive gear system may beincorporated into the gas turbine engine 300 such that the fan 314rotates at a lower speed than does the low speed spool 328. The highpressure turbine first stage spool 330 and the high pressure turbinesecond stage spool 332 are configured to drive the high pressurecompressor 316, which is mounted on the high pressure compressor spool334, via a differential system 340.

In addition, the gas turbine engine 300 includes an augmentation systemwhich, in various embodiments, may include one or more motor-generatorsconfigured to input power to or extract power from various of the spoolswithin the gas turbine engine 300. For example, in various embodiments,a first motor-generator 360 is connected to the high pressure compressorspool 334 and a second motor-generator 362 is connected to the highpressure turbine second stage spool 332. In various embodiments, thefirst motor-generator 360 may comprise an armature 380 that is connectedto the high pressure compressor spool 334 and a stator 381 that isconnected to the engine static structure 338. Similarly, in variousembodiments, the second motor-generator 362 may comprise an armature 382that is connected to the high pressure turbine second stage spool 332and a stator 383 that is connected to the engine static structure 338.The first motor-generator 360 is connected to and controlled by a firstcontroller 364 and the second motor-generator 362 is connected to andcontrolled by a second controller 366. In various embodiments, the firstcontroller 364 and the second controller 366 are further controlled by afull authority digital electric controller or FADEC 368. While the firstcontroller 364, the second controller 366 and the FADEC 368 areillustrated as individual components, the disclosure contemplatescontrol of the first motor-generator 360 and the second motor-generator362 being accomplished by a controller 370, which may be considered toinclude combined functionalities of one or more of the first controller364, the second controller 366 and the FADEC 368. In variousembodiments, an energy storage device 372 is also included within thegas turbine engine 300. The energy storage device 372 may comprise, forexample, a battery, a capacitor or any similar rechargeable energystorage component. In various embodiments, the energy storage device 372may also comprise or be connected to an auxiliary source of power, suchas, for example, an auxiliary power unit or APU 374.

In various embodiments, the controller 370 is configured to monitor andcontrol operation of the first motor-generator 360 and the secondmotor-generator 362, based on whether one or both of themotor-generators are required to drive the spool to which it isattached, to generate power for storage in the energy storage device 372or to carry out load-sharing between the various spools and thecomponents attached thereto. For example, in various embodiments, thefirst motor-generator 360 may be employed to increase (or maintain) therotational speed of the high pressure compressor spool 334 by providingpower to the first motor-generator 360 (i.e., the motor-generator isbeing used as a motor). In various embodiments, the firstmotor-generator 360 may also be employed to decrease (or maintain) therotational speed of the high pressure compressor spool 334 by extractingpower from the first motor-generator 360 (i.e., the motor-generator isbeing used as a generator). Similarly, in various embodiments, thesecond motor-generator 362 may be employed to increase (or maintain) therotational speed of the high pressure turbine second stage spool 332 byproviding power to the second motor-generator 362 (i.e., themotor-generator is being used as a motor). In various embodiments, thesecond motor-generator 362 may also be employed to decrease (ormaintain) the rotational speed of the high pressure turbine second stagespool 332 by extracting power from the second motor-generator 362 (i.e.,the motor-generator is being used as a generator).

Referring more specifically, to FIG. 3B, the differential system 340includes a first stage input gear 342, a second stage input gear 344, afirst stage output gear 345 and a second stage output gear 347. Asillustrated, the first stage input gear 342 is connected to and rotateswith the high pressure turbine first stage spool 330. Similarly, thesecond stage input gear 344 is connected to and rotates with the highpressure turbine second stage spool 332. The first stage output gear 345and the second stage output gear 347 are connected to the high pressurecompressor spool 334 via a shaft 348 or similar mechanism and aredriven, respectively, by the first stage input gear 342 via a firstbevel gear connection 350 and the second stage input gear 344 via asecond bevel gear connection 352. Unlike the first stage input gear 342and the second stage input gear 344, both of which are configured torotate about the central longitudinal axis A, the first stage outputgear 345 and the second stage output gear 347, together with the shaft348 (the combination of which, in various embodiments, is referred to asan output gear assembly), are configured to revolve about the centrallongitudinal axis A in response to being driven by the first stage inputgear 342 and the second stage input gear 344. In addition, asillustrated, the differential system 340 includes a first differentialsubassembly 341 ₁ that comprises the various gears just described. Invarious embodiments, however, the differential system 340 may compriseany number of differential subassemblies, including, for example, asecond differential subassembly 341 ₂, with each of the variousdifferential subassemblies being generally spaced about the centrallongitudinal axis A.

Still referring to FIGS. 3A and 3B, various operational aspects aredescribed. Assume, for example, the first stage input gear 342 has afirst number of input gear teeth, N_(I1), that is proportional to afirst radius, R_(I1), of the first stage input gear 342, while thesecond stage input gear 344 has a second number of input gear teeth,N_(I2), that is proportional to a second radius, R_(I2), of the secondstage input gear 344. Similarly, assume the first stage output gear 345has a first number of output gear teeth, N_(O1), that is proportional toa first radius, R_(O1), of the first stage output gear 345, while thesecond stage output gear 347 has a second number of output gear teeth,N_(O2), that is proportional to a second radius, R_(O2), of the secondstage output gear 347. Assume as well the high pressure turbine firststage spool 330, together with the first stage input gear 342, rotate ata first stage spool rotational speed of N_(HPT1), and the high pressureturbine second stage spool 332, together with the second stage inputgear 344, rotate at a second stage spool rotational speed of N_(HPT2).With such assumptions, the high pressure compressor spool 334 willrotate at a high pressure compressor spool rotational speed of N_(HPC)(or a compressor spool rotational speed), which may be expressed by therelation N_(HPC)=(N_(HPT1)+K*N_(HPT2))/(K+1), whereK=(R_(I2)*R_(O1))/(R_(I1)*R_(O2))=(N_(I2)*N_(O1))/(N_(I1)*N_(O2)). Thus,where the high pressure turbine first stage spool 330 and the highpressure turbine second stage spool 332 are configured to corotate(i.e., rotate in the same direction about the central longitudinal axisA), the high pressure compressor spool rotational speed, N_(HPC), is afunction of the spool speeds N_(HPT1) and N_(HPT2) as well as the gearratios of the differential system 340. Note that where R_(I1)=R_(I2) andR_(O1)=R_(O2), then K=1 and the high pressure compressor spoolrotational speed, N_(HPC), is simply the arithmetic mean of the twoinput spool speeds; or, in other words, where K=1, the differentialsystem 340, as described above, operates as a summer device that isconfigured to split the input rotational speeds of the high pressureturbine first stage spool 330 and the high pressure turbine second stagespool 332.

The general configuration above described enables the first stage 324 ofthe high pressure turbine 320, the second stage 326 of the high pressureturbine 320 and the high pressure compressor 316 to rotate at differentspeeds, such that, for example, N_(HPT1)>N_(HPC)>N_(HPT2). For example,if one assumes N_(I2)=48, N_(I1)=24, N_(O1)=36 and N_(O2)=18, then K=4.Thus, for N_(HPT1)=12,000 rpm (≈1,256 rad/sec) and N_(HPT2)=9,500 rpm(≈995 rad/sec), N_(HPC)=10,000 rpm (≈1,047 rad/sec). Advantageously,then, the configuration enables the high pressure compressor 316 torotate at a speed having a value greater than that which might otherwisebe limited by maximum allowable stress limits within the blades of thesecond stage 326 of the high pressure turbine 320 (e.g., maximumcentrifugal stress states or AN² limits). Further, the configurationenables the first stage 324 of the high pressure turbine 320 to rotateat a speed having a value greater than both those of the high pressurecompressor 316 and the second stage 326 of the high pressure turbine320, enabling the first stage 324 to operate at a higher efficiency thanthat which might otherwise be limited by efficiency or stressconsiderations of the aforementioned rotating components. Also, invarious embodiments, the fan 314 will rotate at a speed equal to that ofthe low pressure turbine 322 via the low speed spool 328.

Consistent with the foregoing description, in various embodiments, thefirst motor-generator 360 and the second motor-generator 362 may beemployed to adjust—e.g., to increase or decrease—one or both of N_(HPC)and N_(HPT2), respectively, by operating one or both of the respectivemotor-generators in either a motor-mode or a generator-mode. Forexample, during transient operation of the gas turbine engine 300—e.g.,during a takeoff or an acceleration in flight—increasing the speed ofone or both of N_(HPC) and N_(HPT2) may result in increased power orefficiency of the engine without approaching or reaching the applicablemaximum centrifugal stress states or AN² limits of the turbine blades,for example, in the second stage 326 of the high pressure turbine 320.On the other hand, during steady state operation—e.g., during cruise ataltitude—adjusting the speed of one or both of N_(HPC) and N_(HPT2) mayresult in increased efficiency of the engine and the ability to generatepower for storage in the storage device.

Referring now to FIGS. 4A and 4B, a gas turbine engine 400 isillustrated, in accordance with various embodiments. As illustrated, thegas turbine engine 400 shares certain of the structural characteristicsof the gas turbine engine 300 described above with reference to FIGS. 3Aand 3B, a principal exception being the addition of a low pressurecompressor 415 to the gas turbine engine 400. Similar to the descriptionabove, the gas turbine engine 400 is a four-spool turbofan engine thatgenerally incorporates a fan section 402, a compressor section 404, acombustor section 406 and a turbine section 408. The fan section 402drives air along a bypass flow path B in a bypass duct defined by aradially inner surface of a nacelle 410 and a radially outer surface ofa core engine case 412, while the compressor section 404 drives airalong a core flow path C for compression and communication into thecombustor section 406 and then expansion through the turbine section408. The core flow path C is generally ducted through a core duct, whichmay be defined by the compressor, combustor and turbine sections,radially inward of the core engine case 412. The core duct may also bedefined, in part, by a forward strut 411, an intermediate strut 413 andan exit strut 417, each of which may also function as a vane or duct andbe formed as part of or connected to a fixed structure for various ofthe rotating components of the gas turbine engine 400.

More specifically, the fan section 402 includes a fan 414, thecompressor section 404 includes the low pressure compressor 415, a highpressure compressor 416, the combustor section 406 includes a combustor418 and the turbine section 408 includes a high pressure turbine 420 anda low pressure turbine 422. Further, the high pressure turbine 420includes a first stage 424 and a second stage 426 disposed downstream ofthe first stage 424. In general, air in the core flow path C iscompressed, first by the low pressure compressor 415 and then by thehigh pressure compressor 416, mixed and burned with fuel in thecombustor 418, and then expanded over the high pressure turbine 420 andthen the low pressure turbine 422, with the high pressure turbine 420and the low pressure turbine 422 being configured, as described below,to drive the low pressure compressor 415, the high pressure compressor416 and the fan 414.

Still referring to FIGS. 4A and 4B, in various embodiments, the gasturbine engine 400 includes a low speed spool 428, a high pressureturbine first stage spool 430, a high pressure turbine second stagespool 432 and a high pressure compressor spool 434. Each of the spoolsis generally situated within a bearing assembly 436, components of whichare housed within or connected to an engine static structure 438, andconfigured to rotate coaxially with respect to a central longitudinalaxis A. The low speed spool 428 is configured to connect the fan 414 tothe low pressure turbine 422. While the low speed spool 428 isillustrated as directly connecting the fan 414 and the low pressureturbine 422, it will be appreciated that various intervening drivesystems, such as, for example, a fan drive gear system may beincorporated into the gas turbine engine 400 such that the fan 414rotates at a lower speed than does the low speed spool 428. The highpressure turbine first stage spool 430 and the high pressure turbinesecond stage spool 432 are configured to drive the high pressurecompressor 416, which is mounted on the high pressure compressor spool434, via a differential system 440. The high pressure turbine secondstage spool 432 is also configured to rotate the low pressure compressor415.

Referring more specifically, to FIG. 4B, the differential system 440includes a first stage input gear 442, a second stage input gear 444, afirst stage output gear 445 and a second stage output gear 447. Asillustrated, the first stage input gear 442 is connected to and rotateswith the high pressure turbine first stage spool 430. Similarly, thesecond stage input gear 444 is connected to and rotates with the highpressure turbine second stage spool 432. The first stage output gear 445and the second stage output gear 447 are connected to the high pressurecompressor spool 434 via a shaft 448 or similar mechanism and aredriven, respectively, by the first stage input gear 442 via a firstbevel gear connection 450 and the second stage input gear 444 via asecond bevel gear connection 452. Unlike the first stage input gear 442and the second stage input gear 444, both of which are configured torotate about the central longitudinal axis A, the first stage outputgear 445 and the second stage output gear 447, together with the shaft448 (the combination of which, in various embodiments, is referred to asan output gear assembly), are configured to revolve about the centrallongitudinal axis A in response to being driven by the first stage inputgear 442 and the second stage input gear 444. In addition, asillustrated, the differential system 440 includes a first differentialsubassembly 441 ₁ that comprises the various gears just described. Invarious embodiments, however, the differential system 440 may compriseany number of differential subassemblies, including, for example, asecond differential subassembly 441 ₂, with each of the variousdifferential subassemblies being generally spaced about the centrallongitudinal axis A.

In addition, the gas turbine engine 400 includes an augmentation systemwhich, in various embodiments, may include one or more motor-generatorsconfigured to input power to or extract power from various of the spoolswithin the gas turbine engine 400. For example, in various embodiments,a first motor-generator 460 is connected to the high pressure compressorspool 434, a second motor-generator 462 is connected to the highpressure turbine second stage spool 432 and a third motor-generator 461is connected to the low speed spool 428 and to the high pressure turbinesecond stage spool 432. In various embodiments, the firstmotor-generator 460 may comprise an armature 480 that is connected tothe high pressure compressor spool 434 and a stator 481 that isconnected to the engine static structure 438. Similarly, in variousembodiments, the second motor-generator 462 may comprise an armature 482that is connected to the high pressure turbine second stage spool 432and a stator 483 that is connected to the engine static structure 438.Also, in various embodiments, the third motor-generator 461 may comprisean armature 484 that is connected to the high pressure turbine secondstage spool 432 and a stator 485 that is connected to the low speedspool 428, enabling both the armature 484 and the stator 485 to rotate,but at different speeds such that a motor-like or generator-likeoperation may be affected between the high pressure turbine second stagespool 432 and the low speed spool 428. The first motor-generator 460 isconnected to and controlled by a first controller 464, the secondmotor-generator 462 is connected to and controlled by a secondcontroller 466 and the third motor-generator 461 is connected to andcontrolled by a third controller 465. In various embodiments, the firstcontroller 464, the second controller 466 and the third controller 465are further controlled by a full authority digital electric controlleror FADEC 468. While the first controller 464, the second controller 466,the third controller 465 and the FADEC 468 are illustrated as individualcomponents, the disclosure contemplates control of the firstmotor-generator 460, the second motor-generator 462 and the thirdmotor-generator 461 being accomplished by a controller 470, which may beconsidered to include combined functionalities of one or more of thefirst controller 464, the second controller 466, the third controller465 and the FADEC 468. In various embodiments, an energy storage device472 is also included within the gas turbine engine 400. The energystorage device 472 may comprise, for example, a battery, a capacitor orany similar rechargeable energy storage component. In variousembodiments, the energy storage device 472 may also comprise or beconnected to an auxiliary source of power, such as, for example, anauxiliary power unit or APU 474.

In various embodiments, the controller 470 is configured to monitor andcontrol operation of the first motor-generator 460, the secondmotor-generator 462 and the third motor-generator 461, based on whetherone or more of the motor-generators are required to drive the spool towhich it is attached, to generate power for storage in the energystorage device 472 or to carry out load-sharing between the variousspools and the components attached thereto. For example, in variousembodiments, the first motor-generator 460 may be employed to increase(or maintain) the rotational speed of the high pressure compressor spool434 by providing power to the first motor-generator 460 (i.e., themotor-generator is being used as a motor). In various embodiments, thefirst motor-generator 460 may also be employed to decrease (or maintain)the rotational speed of the high pressure compressor spool 434 byextracting power from the first motor-generator 460 (i.e., themotor-generator is being used as a generator). Similarly, in variousembodiments, the second motor-generator 462 may be employed to increase(or maintain) the rotational speed of the high pressure turbine secondstage spool 432 by providing power to the second motor-generator 462(i.e., the motor-generator is being used as a motor). In variousembodiments, the second motor-generator 462 may also be employed todecrease (or maintain) the rotational speed of the high pressure turbinesecond stage spool 432 by extracting power from the secondmotor-generator 462 (i.e., the motor-generator is being used as agenerator). In addition, in various embodiments, the thirdmotor-generator 461 may be employed to increase (or maintain) therotational speed of the high pressure turbine second stage spool 432 byproviding power to the third motor-generator 461 (i.e., themotor-generator is being used as a motor). In various embodiments, thethird motor-generator 461 may also be employed to decrease (or maintain)the rotational speed of the high pressure turbine second stage spool 432by extracting power from the third motor-generator 461 (i.e., themotor-generator is being used as a generator).

Still referring to FIGS. 4A and 4B, various operational aspects aredescribed. Assume, for example, the first stage input gear 442 has afirst number of input gear teeth, N_(I1), that is proportional to afirst radius, R_(I1), of the first stage input gear 442, while thesecond stage input gear 444 has a second number of input gear teeth,N_(I2), that is proportional to a second radius, R_(I2), of the secondstage input gear 444. Similarly, assume the first stage output gear 445has a first number of output gear teeth, N_(O1), that is proportional toa first radius, R_(O1), of the first stage output gear 445, while thesecond stage output gear 447 has a second number of output gear teeth,N_(O2), that is proportional to a second radius, R_(O2), of the secondstage output gear 447. Assume as well the high pressure turbine firststage spool 430, together with the first stage input gear 442, rotate ata first stage spool rotational speed of N_(HPT1), and the high pressureturbine second stage spool 432, together with the second stage inputgear 444, rotate at a second stage spool rotational speed of N_(HPT2).With such assumptions, the high pressure compressor spool 434 willrotate at a high pressure compressor spool rotational speed of N_(HPC)(or a compressor spool rotational speed), which may be expressed by therelation N_(HPC)=(N_(HPT1)+K*N_(HPT2))/(K+1), whereK=(R_(I2)*R_(O1))/(R_(I1)*R_(O2))=(N_(I2)*N_(O1))/(N_(I1)*N_(O2)). Thus,where the high pressure turbine first stage spool 430 and the highpressure turbine second stage spool 432 are configured to corotate(i.e., rotate in the same direction about the central longitudinal axisA), the high pressure compressor spool rotational speed, N_(HPC), is afunction of the spool speeds N_(HPT1) and N_(HPT2) as well as the gearratios of the differential system 440. Note that where R_(I1)=R_(I2) andR_(O1)=R_(O2), then K=1 and the high pressure compressor spoolrotational speed, N_(HPC), is simply the arithmetic mean of the twoinput spool speeds; or, in other words, where K=1, the differentialsystem 440, as described above, operates as a summer device that isconfigured to split the input rotational speeds of the high pressureturbine first stage spool 430 and the high pressure turbine second stagespool 432.

The general configuration above described enables the first stage 424 ofthe high pressure turbine 420, the second stage 426 of the high pressureturbine 420 and the high pressure compressor 416 to rotate at differentspeeds, such that, for example, N_(HPT1)>N_(HPC)>N_(HPT2). For example,if one assumes N_(I2)=48, N_(I1)=24, N_(O1)=36 and N_(O2)=18, then K=4.Thus, for N_(HPT1)=12,000 rpm (≈1,256 rad/sec) and N_(HPT2)=9,500 rpm(≈995 rad/sec), N_(HPC)=10,000 rpm (≈1,047 rad/sec). Advantageously,then, the configuration enables the high pressure compressor 416 torotate at a speed having a value greater than that which might otherwisebe limited by maximum allowable stress limits within the blades of thesecond stage 426 of the high pressure turbine 420 (e.g., maximumcentrifugal stress states or AN² limits). Further, the configurationenables the first stage 424 of the high pressure turbine 420 to rotateat a speed having a value greater than both those of the high pressurecompressor 416 and the second stage 426 of the high pressure turbine420, enabling the first stage 424 to operate at a higher efficiency thanthat which might otherwise be limited by efficiency or stressconsiderations of the aforementioned rotating components. Also, invarious embodiments, the fan 414 will rotate at a speed equal to that ofthe low pressure turbine 422 via the low speed spool 428, while the lowpressure compressor 415 will rotate at a speed equal to N_(HPT2) via thehigh pressure turbine second stage spool 432.

Consistent with the foregoing description, in various embodiments, thefirst motor-generator 460, the second motor-generator 462 and the thirdmotor-generator 461 may be employed to adjust—e.g., to increase ordecrease—one or both of N_(HPC) and N_(HPT2), respectively, by operatingone or more of the respective motor-generators in either a motor-mode ora generator-mode. For example, during transient operation of the gasturbine engine 400—e.g., during a takeoff or an acceleration inflight—increasing the speed of one or both of N_(HPC) and N_(HPT2) mayresult in increased power or efficiency of the engine withoutapproaching or reaching the applicable maximum centrifugal stress statesor AN² limits of the turbine blades, for example, in the second stage426 of the high pressure turbine 420. On the other hand, during steadystate operation—e.g., during cruise at altitude—adjusting the speed ofone or both of N_(HPC) and N_(HPT2) may result in increased efficiencyof the engine and the ability to generate power for storage in thestorage device. Further, in various embodiments and as illustrated anddescribed herein, the torque split differential, where K>1, enablescustomization of splitting the speeds and the power outputs of the firststage 424 of the high pressure turbine 420 and the second stage 426 ofthe high pressure turbine 420, which drive the high pressure compressor416 and the low pressure compressor 415, and the first motor-generator460 (connected to the high pressure compressor spool 434), the secondmotor-generator 462 (connected to the high pressure turbine second stagespool 432) and the third motor-generator 461 (connected to the low speedspool 428 and to the high pressure turbine second stage spool 432). Thecustomization of speeds also applies to the high pressure turbine secondstage spool 432 and the low speed spool 428 to improve the designefficiency of the third motor-generator 461. The foregoing also enablesenhanced load sharing between the high pressure turbine first stagespool 430, the high pressure turbine second stage spool 432 and the lowspeed spool 428, providing higher power outputs to the high pressurecompressor spool 434 and the low speed spool 428, enabling faster spoolup during transient operation. Additionally, in various embodiments andas illustrated and described, where the rotational speed of the lowpressure compressor 415, N_(LPC), is less than N_(HPC), and the lowpressure compressor 415 is not coupled to the fan 414 (e.g., through ashaft or fan drive gear system connected to the low pressure compressor415), N_(LPC) becomes independent of the rotational speed of the fan414, N_(FAN). This facilitates an increase in the pressure ratio acrossthe low pressure compressor 415, leading to an increase in the overallpressure ratio across the compressor section 404, including both the lowpressure compressor 415 and the high pressure compressor 416. In variousembodiments, the benefits and advantages described herein are enhancedas the value of K becomes substantially greater than unity.

Referring now to FIG. 5, a method 500 for distributing power from aturbine section of a gas turbine engine (or, in various embodiments, amethod of distributing power within a gas turbine engine) is described.In various embodiments, a first step 502 includes generating a firststage rotational power from a first stage of the turbine section. Asecond step 504 includes generating a second stage rotational power froma second stage of the turbine section. A third step 506 includesinputting the first stage rotational power and the second stagerotational power into a differential system, such as, for example, oneof the differential system 140 described above with reference to FIGS.1A and 1B or the differential system 240 described above with referenceto FIGS. 2A and 2B, the differential system 340 described above withreference to FIGS. 3A and 3B or the differential system 440 describedabove with reference to FIGS. 4A and 4B. In various embodiments,inputting the first stage rotational power and the second stagerotational power into a differential system is performed via a firststage spool and a second stage spool, such as, for example, the highpressure turbine first stage spool 130 and the high pressure turbinesecond stage spool 132 described above with reference to FIGS. 1A and1B, the high pressure turbine first stage spool 230 and the highpressure turbine second stage spool 232 described above with referenceto FIGS. 2A and 2B, the high pressure turbine first stage spool 330 andthe high pressure turbine second stage spool 332 described above withreference to FIGS. 3A and 3B and the high pressure turbine first stagespool 430 and the high pressure turbine second stage spool 432 describedabove with reference to FIGS. 4A and 4B. A fourth step 508 includesoutputting from the differential system a compressor stage rotationalpower configured to drive a compressor section of the gas turbineengine. In various embodiments, the method 500 further includes drivinga low pressure compressor of the compressor section via the second stagerotational power. In various embodiments, the method 500 furtherincludes driving a fan via a low pressure turbine of the turbinesection.

In various embodiments, the first stage rotational power from the firststage of the turbine section may be defined as the torque, τ, generatedat a high pressure turbine first stage spool multiplied by therotational speed, N, of the spool. For example, in various embodiments,the first stage rotational power may represent the product of the torqueand the rotational speed of a high pressure turbine first stage spool,such as, for example, the high pressure turbine first stage spool 130described above with reference to FIGS. 1A and 1B, the high pressureturbine first stage spool 230 described above with reference to FIGS. 2Aand 2B, the high pressure turbine first stage spool 330 described abovewith reference to FIGS. 3A and 3B or the high pressure turbine firststage spool 430 described above with reference to FIGS. 4A and 4B (e.g.,P_(HPT1)=τ_(HPT1)×π/30×N_(HPT1)). Similarly, the second stage rotationalpower from the second stage of the turbine section may be defined as thetorque, τ, generated at a high pressure turbine second stage spoolmultiplied by the rotational speed, N, of the spool. For example, invarious embodiments, the second stage rotational power may represent theproduct of the torque and the rotational speed of a high pressureturbine second stage spool, such as, for example, the high pressureturbine second stage spool 132 described above with reference to FIGS.1A and 1B, the high pressure turbine second stage spool 232 describedabove with reference to FIGS. 2A and 2B, the high pressure turbinesecond stage spool 332 described above with reference to FIGS. 3A and 3Bor the high pressure turbine second stage spool 432 described above withreference to FIGS. 4A and 4B (e.g., P_(HPT2)=τ_(HPT2)×π/30×N_(HPT2)). Inaddition, the compressor stage rotational power configured to drive thecompressor section of the gas turbine engine may be defined as thetorque, τ, input at a compressor section spool multiplied by therotational speed, N, of the spool. For example, in various embodiments,the compressor stage rotational power may represent the product of thetorque and the rotational speed of a high pressure compressor spool,such as, for example, the high pressure compressor spool 134 describedabove with reference to FIGS. 1A and 1B, the high pressure compressorspool 234 described above with reference to FIGS. 2A and 2B, the highpressure compressor spool 334 described above with reference to FIGS. 3Aand 3B or the high pressure compressor spool 434 described above withreference to FIGS. 4A and 4B (e.g., P_(HPC)=τ_(HPC)×π/30×N_(HPC)). Inthe foregoing relations for power, the rotational speed of the spool, N,is typically provided in rotations per minute, with the factor π/30 usedto convert the rotational speed to radians per second.

Referring now to FIGS. 6A and 6B, results and benefits of variousembodiments are provided in the form of a graph 600 illustrating themechanical power used to drive a high pressure compressor (y-axis)versus the thermal power required to drive a high pressure turbine(x-axis). The results provided in the graph 600 are consistent withoperation of the gas turbine engine 100 described above with referenceto FIGS. 1A and 1B, which includes the high pressure turbine first stagespool 130, the high pressure turbine second stage spool 132 and the highpressure compressor spool 134. With this configuration, the highpressure compressor spool 134 is driven primarily via the output of thedifferential system 140, though power to drive the high pressurecompressor spool 134 may be supplemented by the first motor-generator160 connected to the high pressure compressor spool 134 or the secondmotor-generator 162 connected to the high pressure turbine second stagespool 132, both of which are coupled to the energy storage device 172.Stated otherwise, in various embodiments, the high pressure compressorspool 134 is configured to receive an auxiliary input power (e.g., anelectrical power) via the first motor-generator 160 connected to thehigh pressure compressor spool 134 (e.g., a first input power) or thesecond motor-generator 162 connected to the high pressure turbine secondstage spool 132 (e.g., a second input power), both of which are coupledto the energy storage device 172. As indicated below, the auxiliaryinput power enables a reduced fuel power used to drive the high pressureturbine 120 via an exhaust stream from the combustor 118. When notproviding or supplementing power to drive the high pressure compressorspool 134, the first motor-generator 160 or the second motor-generator162 may be used to charge the energy storage device 172. Statedotherwise, when not providing or supplementing power to drive the highpressure compressor spool 134, the first motor-generator 160 or thesecond motor-generator 162 may be used to extract an auxiliary outputpower to charge the energy storage device 172, where the firstmotor-generator 160 is used to extract a first output power and thesecond motor-generator 162 is used to extract a second output power.

As illustrated in the graph 600, for this configuration, where K=1, thepower and torque input to the differential system 140 by the highpressure turbine second stage spool 132 and the second motor-generator162 is equal to the power and torque input to the differential system140 by the high pressure turbine first stage spool 130. By way ofexample, plotted on the graph 600 are several core system power curves,including a compressor spool power curve 601, a first stage spool powercurve 602, and a second stage spool power curve 603. Also plotted on thegraph 600 are several auxiliary system power curves, including a totalauxiliary power curve 604, a first motor-generator power curve 605 and asecond motor-generator power curve 606. The units of power shown on thegraph are dimensionless and intended to illustrate the overall powerbalance within the system at various loads required to drive the highpressure compressor spool 134 which, in turn, drives the high pressurecompressor 116 illustrated in FIG. 1A.

For example, where the high pressure compressor spool 134 requires 12.0units of power to drive the high pressure compressor 116 (which may beconsidered consistent with a takeoff phase of flight), the input fuelpower, which represents the thermal energy of the exhaust exiting thecombustor 118 and converted via the high pressure turbine 120 intorotational power at the high pressure turbine first stage spool 130 andthe high pressure turbine second stage spool 132, is 11.0 units ofpower. The remaining 1.0 units of power required to drive the highpressure compressor spool 134 is provided by the second motor-generator162 connected to the high pressure turbine second stage spool 132. Thisis illustrated in the graph 600 by the various power curves.Specifically, the compressor spool power curve 601 indicates 12.0 unitsof power, the first stage spool power curve 602 indicates 6.0 units ofpower, the second stage spool power curve 603 indicates 5.0 units ofpower and the total auxiliary power curve 604 indicates 1.0 units ofpower (the first motor-generator power curve 605 indicates 0.0 units ofpower and the second motor-generator power curve 606 indicates 1.0 unitsof power).

Still referring to FIG. 6A, where the high pressure compressor spool 134requires 6.0 units of power to drive the high pressure compressor 116(which may be considered consistent with a climb phase of flight), theinput fuel power is 7.0 units of power. The excess 1.0 units of powerrequired to drive the high pressure compressor spool 134 is used by thefirst motor-generator 160 connected to the high pressure compressorspool 134 to charge the energy storage device 172. This is illustratedin the graph 600 by the various power curves. Specifically, thecompressor spool power curve 601 indicates 6.0 units of power, the firststage spool power curve 602 indicates 3.5 units of power, the secondstage spool power curve 603 indicates 3.5 units of power and the totalauxiliary power curve 604 indicates negative 1.0 units of power (thefirst motor-generator power curve 605 indicates −1.0 units of power andthe second motor-generator power curve 606 indicates 0.0 units ofpower).

Similarly, where the high pressure compressor spool 134 requires 1.5units of power to drive the high pressure compressor 116 (which may beconsidered consistent with a cruise phase of flight), the input fuelpower is 4.5 units of power. The excess 3.0 units of power required todrive the high pressure compressor spool 134 is used by both the firstmotor-generator 160 connected to the high pressure compressor spool 134and the second motor-generator 162 connected to the high pressureturbine second stage spool 132 to charge the energy storage device 172.This is illustrated in the graph 600 by the various power curves.Specifically, the compressor spool power curve 601 indicates 1.5 unitsof power, the first stage spool power curve 602 indicates 1.75 units ofpower, the second stage spool power curve 603 indicates 2.75 units ofpower and the total auxiliary power curve 604 indicates negative 3.0units of power (the first motor-generator power curve 605 indicates −2.0units of power and the second motor-generator power curve 606 indicates−1.0 units of power).

The foregoing data is provided for a configuration in which the energystorage device 172 may be represented as a baseline storage devicehaving a baseline storage or utilization capacity which, for example,may be assumed equal to 3.0 units, with 1.0 units being used during thetakeoff mode. Referring to FIG. 6B, the graph 600 is illustrated withthe power curves for the baseline data just described, together with asecond set of power curves for the energy storage device 172 having autilization capacity of 2.0 units, with 3.0 units being used during thetakeoff mode, and a third set of power curves for the storage devicehaving a utilization capacity of 3.0 units, with 3.0 units being usedduring the takeoff mode. In various embodiments, the energy storagedevice 172 may be considered a battery having three cells, with eachcell having a storage or usage capacity equal to 1.0 units. Similar tothe foregoing, the second set of power curves (and the third set ofpower curves) will include a compressor spool power curve 611 (and 621),a first stage spool power curve 612 (and 622), a second stage spoolpower curve 613 (and 623), a total auxiliary power curve 614 (and 624),a first motor-generator power curve 615 (and 625) and a secondmotor-generator power curve 616 (and 626). The combined results for eachof the three sets of power curves are summarized in the following table:

K = 1 HPC Fuel 1^(st) Spool 2^(nd) Spool Total Aux 1^(st) M-G 2^(nd) M-GMode Utilization Capacity = 3.0 Units 12.00 9.00 5.00 4.00 3.00 2.001.00 Takeoff 6.00 5.00 2.50 2.50 1.00 1.00 0.00 Climb 1.50 2.50 0.751.75 −1.00 0.00 −1.00 Cruise Utilization Capacity = 2.0 Units 12.00 10.05.50 4.50 2.00 1.00 1.00 Takeoff 6.00 6.00 3.00 3.00 0.00 0.00 0.00Climb 1.50 3.50 1.25 2.25 −2.00 −1.00 −1.00 Cruise Utilization Capacity= 1.0 Units 12.00 11.00 6.00 5.00 1.00 0.00 1.00 Takeoff 6.00 7.00 3.503.50 −1.00 −1.00 0.00 Climb 1.50 4.50 1.75 2.75 −3.00 −2.00 −1.00 Cruise

Referring now to FIGS. 7A and 7B, results and benefits of variousembodiments are provided in the form of a graph 700 illustrating themechanical power used to drive a high pressure compressor (y-axis)versus the thermal power required to drive a high pressure turbine(x-axis). The results provided in the graph 700 are consistent withoperation of the gas turbine engine 300 described above with referenceto FIGS. 3A and 3B, which includes the high pressure turbine first stagespool 330, the high pressure turbine second stage spool 332 and the highpressure compressor spool 334. With this configuration, the highpressure compressor spool 334 is driven primarily via the output of thedifferential system 340, though power to drive the high pressurecompressor spool 334 may be supplemented by the first motor-generator360 connected to the high pressure compressor spool 334 or the secondmotor-generator 362 connected to the high pressure turbine second stagespool 332, both of which are coupled to the energy storage device 372.Stated otherwise, in various embodiments, the high pressure compressorspool 334 is configured to receive an auxiliary input power (e.g., anelectrical power) via the first motor-generator 360 connected to thehigh pressure compressor spool 334 (e.g., a first input power) or thesecond motor-generator 362 connected to the high pressure turbine secondstage spool 332 (e.g., a second input power), both of which are coupledto the energy storage device 372. As indicated below, the auxiliaryinput power enables a reduced fuel power used to drive the high pressureturbine 320 via an exhaust stream from the combustor 318. When notproviding or supplementing power to drive the high pressure compressorspool 334, the first motor-generator 360 or the second motor-generator362 may be used to charge the energy storage device 372. Statedotherwise, when not providing or supplementing power to drive the highpressure compressor spool 334, the first motor-generator 360 or thesecond motor-generator 362 may be used to extract an auxiliary outputpower to charge the energy storage device 372, where the firstmotor-generator 360 is used to extract a first output power and thesecond motor-generator 362 is used to extract a second output power.

As illustrated in the graph 700, for this configuration, where K=2, thepower and torque input to the differential system 340 by the highpressure turbine second stage spool 332 and the second motor-generator362 is twice the power and torque input to the differential system 340by the high pressure turbine first stage spool 330. By way of example,plotted on the graph 700 are several core system power curves, includinga compressor spool power curve 701, a first stage spool power curve 702,and a second stage spool power curve 703. Also plotted on the graph 700are several auxiliary system power curves, including a total auxiliarypower curve 704, a first motor-generator power curve 705 and a secondmotor-generator power curve 706. The units of power shown on the graphare dimensionless and intended to illustrate the overall power balancewithin the system at various loads required to drive the high pressurecompressor spool 334 which, in turn, drives the high pressure compressor316 illustrated in FIG. 3A.

For example, where the high pressure compressor spool 334 requires 12.0units of power to drive the high pressure compressor 316 (which may beconsidered consistent with a takeoff phase of flight), the input fuelpower, which represents the thermal energy of the exhaust exiting thecombustor 318 and converted via the high pressure turbine 320 intorotational power at the high pressure turbine first stage spool 330 andthe high pressure turbine second stage spool 332, is 11.0 units ofpower. The remaining 1.0 units of power required to drive the highpressure compressor spool 334 is provided by the second motor-generator362 connected to the high pressure turbine second stage spool 332. Thisis illustrated in the graph 700 by the various power curves.Specifically, the compressor spool power curve 701 indicates 12.0 unitsof power, the first stage spool power curve 702 indicates 4.0 units ofpower, the second stage spool power curve 703 indicates 7.0 units ofpower and the total auxiliary power curve 704 indicates 1.0 units ofpower (the first motor-generator power curve 705 indicates 0.0 units ofpower and the second motor-generator power curve 706 indicates 1.0 unitsof power).

Still referring to FIG. 7A, where the high pressure compressor spool 334requires 6.0 units of power to drive the high pressure compressor 316(which may be considered consistent with a climb phase of flight), theinput fuel power is 7.0 units of power. The excess 1.0 units of powerrequired to drive the high pressure compressor spool 334 is used by thefirst motor-generator 360 connected to the high pressure compressorspool 334 to charge the energy storage device 372. This is illustratedin the graph 700 by the various power curves. Specifically, thecompressor spool power curve 701 indicates 6.0 units of power, the firststage spool power curve 702 indicates 2.333 units of power, the secondstage spool power curve 703 indicates 4.667 units of power and the totalauxiliary power curve 704 indicates negative 1.0 units of power (thefirst motor-generator power curve 705 indicates −1.0 units of power andthe second motor-generator power curve 706 indicates 0.0 units ofpower).

Similarly, where the high pressure compressor spool 334 requires 1.5units of power to drive the high pressure compressor 316 (which may beconsidered consistent with a cruise phase of flight), the input fuelpower is 4.5 units of power. The excess 3.0 units of power required todrive the high pressure compressor spool 334 is used by both the firstmotor-generator 360 connected to the high pressure compressor spool 334and the second motor-generator 362 connected to the high pressureturbine second stage spool 332 to charge the energy storage device 372.This is illustrated in the graph 700 by the various power curves.Specifically, the compressor spool power curve 701 indicates 1.5 unitsof power, the first stage spool power curve 702 indicates 1.167 units ofpower, the second stage spool power curve 703 indicates 3.333 units ofpower and the total auxiliary power curve 704 indicates negative 3.0units of power (the first motor-generator power curve 705 indicates −2.0units of power and the second motor-generator power curve 706 indicates−1.0 units of power).

The foregoing data is provided for a configuration in which the energystorage device 372 may be represented as a baseline storage devicehaving a baseline storage or utilization capacity which, for example,may be assumed equal to 3.0 units, with 1.0 units being used during thetakeoff mode. Referring to FIG. 7B, the graph 700 is illustrated withthe power curves for the baseline data just described, together with asecond set of power curves for the energy storage device 372 having autilization capacity of 2.0 units, with 2.0 units being used during thetakeoff mode, and a third set of power curves for the storage devicehaving a utilization capacity of 3.0 units, with 3.0 units being usedduring the takeoff mode. In various embodiments, the energy storagedevice 372 may be considered a battery having three cells, with eachcell having a storage or usage capacity equal to 1.0 units. Similar tothe foregoing, the second set of power curves (and the third set ofpower curves) will include a compressor spool power curve 711 (and 721),a first stage spool power curve 712 (and 722), a second stage spoolpower curve 713 (and 723), a total auxiliary power curve 714 (and 724),a first motor-generator power curve 715 (and 725) and a secondmotor-generator power curve 716 (and 726). The combined results for eachof the three sets of power curves are summarized in the following table:

K = 2 HPC Fuel 1^(st) Spool 2^(nd) Spool Total Aux 1^(st) M-G 2^(nd) M-GMode Utilization Capacity = 3.0 Units 12.00 9.00 3.333 5.667 3.00 2.001.00 Takeoff 6.00 5.00 1.667 3.333 1.00 1.00 0.00 Climb 1.50 2.50 0.5002.000 −1.00 0.00 −1.00 Cruise Utilization Capacity = 2.0 Units 12.0010.0 3.667 6.333 2.00 1.00 1.00 Takeoff 6.00 6.00 2.000 4.000 0.00 0.000.00 Climb 1.50 3.50 0.833 2.667 −2.00 −1.00 −1.00 Cruise UtilizationCapacity = 1.0 Units 12.00 11.00 4.000 7.000 1.00 0.00 1.00 Takeoff 6.007.00 2.333 4.667 −1.00 −1.00 0.00 Climb 1.50 4.50 1.167 3.333 −3.00−2.00 −1.00 Cruise

One or more benefits achieved through the above disclosure may begleaned with further reference to the above tables. Referring to thetable for K=1, for example, a fractional fuel savings is realized forthe climb mode when auxiliary power is input to the high pressurecompressor spool 134. For example, during the climb mode, 6.0 units ofpower is required to drive the high pressure compressor 116. When noauxiliary power is input to either the first motor-generator 160connected to the high pressure compressor spool 134 or the secondmotor-generator 162 connected to the high pressure turbine second stagespool 132, the power from fuel required to drive the high pressurecompressor 116 is also 6.0 units. However, when 1.0 units of power isinput to the first motor-generator 160, the power from fuel required todrive the high pressure compressor 116 is reduced to 5.0 units,providing a fractional fuel savings of 16.667%. The change of powerinput by the first motor-generator 160 and the change of powerextraction by the first motor-generator 160 is the same as the change infuel power. In this mode of climb, switching from charging the energystorage device 172 at 1.0 units of power to discharging the energystorage device 172 at 1.0 units of power changes the required fuel powerfrom 7.0 units of power to 5.0 units of power. This switching of powerrepresents a fractional change of 2.0/7.0, or about a 28.6% reduction infuel power required for the climb mode at constant 6.0 units of power todrive the high pressure compressor 116. The same fractional fuel savingsis achieved for the case where K=2. However, note that in the K=2 case,the power required to drive the high pressure compressor spool 334 andthe high pressure turbine second stage spool 332 is distributed suchthat 66.6% of the required power is input to the high pressure turbinesecond stage spool 332 and 33.3% of the required power is input to thehigh pressure compressor spool 334, whereas in the K=1 case, the powerrequired to drive the high pressure compressor spool 134 and the highpressure turbine second stage spool 132 is evenly split such that 50.0%of the required power is input to the high pressure turbine second stagespool 132 and 50.0% of the required power is input to the high pressurecompressor spool 134. The torque split differential and the first andsecond motor-generators, for both cases K=1 and K=2, enable asubstantially stable inertia of the high pressure turbine second stagespool and a large increase of the high pressure turbine first stagespool and the high pressure compressor power during a wide range ofengine maneuvers—e.g., from cruise to climb modes or from cruise orclimb to takeoff (e.g., transient operation during flight) modes.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,”“various embodiments,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f) unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises,”“comprising,” or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

Finally, it should be understood that any of the above describedconcepts can be used alone or in combination with any or all of theother above described concepts. Although various embodiments have beendisclosed and described, one of ordinary skill in this art wouldrecognize that certain modifications would come within the scope of thisdisclosure. Accordingly, the description is not intended to beexhaustive or to limit the principles described or illustrated herein toany precise form. Many modifications and variations are possible inlight of the above teaching.

What is claimed:
 1. A method of distributing power within a gas turbineengine, comprising: driving a high pressure turbine having a first stageand a second stage with an exhaust stream from a combustor, the firststage connected to a high pressure turbine first stage spool and thesecond stage connected to a high pressure turbine second stage spool;driving a high pressure compressor connected to a high pressurecompressor spool via a differential system, the differential systemhaving a first stage input gear connected to the high pressure turbinefirst stage spool, a second stage input gear connected to the highpressure turbine second stage spool and an output gear assemblyconnected to the high pressure compressor spool; and selectivelyapplying an auxiliary input power into at least one of the high pressurecompressor spool and the high pressure turbine.
 2. The method of claim1, wherein the selectively applying the auxiliary input power includesapplying a first input power to a first motor-generator connected to thehigh pressure compressor spool.
 3. The method of claim 1, wherein theselectively applying the auxiliary input power includes applying asecond input power to a second motor-generator connected to the highpressure turbine second stage spool.
 4. The method of claim 1, whereinthe selectively applying the auxiliary input power includes applying afirst input power to a first motor-generator connected to the highpressure compressor spool and a second input power to a secondmotor-generator connected to the high pressure turbine second stagespool.
 5. The method of claim 1, further comprising selectivelyextracting an auxiliary output power from at least one of the highpressure compressor spool and the high pressure turbine.
 6. The methodof claim 5, wherein the selectively extracting the auxiliary outputpower includes charging a storage device.
 7. The method of claim 5,wherein the selectively extracting the auxiliary output power includesextracting a first output power from a first motor-generator connectedto the high pressure compressor spool.
 8. The method of claim 5, whereinthe selectively extracting the auxiliary output power includesextracting a second output power from a second motor-generator connectedto the high pressure turbine second stage spool.
 9. The method of claim5, wherein the selectively extracting the auxiliary output powerincludes extracting a first output power from a first motor-generatorconnected to the high pressure compressor spool and a second outputpower from a second motor-generator connected to the high pressureturbine second stage spool.
 10. The method of claim 5, wherein theauxiliary input power comprises an electrical power from a storagedevice.
 11. The method of claim 10, wherein the auxiliary input powerenables a reduced fuel power used to drive the high pressure turbine.12. A gas turbine engine, comprising: a turbine having a first stage anda second stage, the first stage connected to a first stage spool and thesecond stage connected to a second stage spool; a compressor connectedto a compressor spool; a differential system having a first stage inputgear connected to the first stage spool, a second stage input gearconnected to the second stage spool and an output gear assemblyconnected to the compressor spool; and an augmentation system configuredto input power into at least one of the compressor spool and theturbine.
 13. The gas turbine engine of claim 12, wherein thedifferential system is configured to drive the compressor spool inresponse to the first stage spool and the second stage spool rotating atdifferent speeds with respect to a central longitudinal axis.
 14. Thegas turbine engine of claim 13, wherein the differential system isconfigured to input a first stage spool rotational speed and a secondstage spool rotational speed and output a compressor spool rotationalspeed having a value in between the first stage spool rotational speedand the second stage spool rotational speed.
 15. The gas turbine engineof claim 13, wherein the differential system is configured to input afirst stage spool rotational speed greater than a second stage spoolrotational speed and output a compressor spool rotational speed having avalue in between the first stage spool rotational speed and the secondstage spool rotational speed.
 16. The gas turbine engine of claim 12,wherein the augmentation system includes a first motor-generatorconnected to the compressor spool and a second motor-generator connectedto the second stage spool.
 17. The gas turbine engine of claim 16,wherein the first motor-generator and the second motor-generator eachinclude a stator connected to an engine static structure.
 18. A methodfor distributing power from a turbine section of a gas turbine engine,comprising: generating a first stage rotational power from a first stageof the turbine section; generating a second stage rotational power froma second stage of the turbine section; inputting into a differentialsystem the first stage rotational power via a first stage spool and thesecond stage rotational power via a second stage spool; outputting fromthe differential system a compressor stage rotational power configuredto drive a compressor spool of the gas turbine engine; and selectivelyapplying an auxiliary input power into at least one of the compressorspool, the first stage spool and the second stage spool.
 19. The methodof claim 18, further comprising selectively extracting an auxiliaryoutput power from at least one of the compressor spool, the first stagespool and the second stage spool.
 20. The method of claim 19, furthercomprising driving a fan via a low pressure turbine of the turbinesection.